This invention relates to engagement timing devices for fluid operated friction devices, and more particularly, to such timing devices utilizing an accumulator and flow restrictions.
Prior art devices have generally provided a single orifice control and accumulator for controlling the engagement timing of a friction device. These control mechanisms have the friction devices and the accumulator downstream of the orifice. This requires that the accumulator be of sufficient volume to accommodate the pressurizing time of the friction devices at a flow rate through the orifice that produces an acceptable fill and stroke time.
These devices further require that the size of the orifice be sufficiently large to provide an acceptable short fill and stroke time and is therefore a compromise to the preferred orifice size. There have been other proposed control mechanisms that provide a secondary pressure control valve to provide rapid filling of the friction device followed by controlled engagement timing. In these devices, the valve controls the pressure to the friction device in such a manner as to permit fluid flow to the accumulator to control a pressure drop through a restriction which in turn establishes the fluid flow level through the valve.
These control devices require a separate valve and accumulator structure with the valve structure requiring a bore, spring and valve spool. Furthermore, these structures generally have two control or feedback chambers, one of which is sensitive to clutch pressure and the other of which is sensitive to fluid flow to the accumulator.